EP2813480A1 - Cement system, comprising accelerator particles coated with cross-linked shellac - Google Patents

Abstract

A cementitious system comprising cross-linked shellac-coated accelerator particles, the use of an additive component containing the crosslinked shellac-coated promoter particles, and a cement slurry comprising the cementitious system and water are proposed.

Description

The present invention relates to a cementitious system comprising crosslinked shellac-coated accelerator particles, the use of an additive component containing the crosslinked shellac-coated accelerator particles, and a cement slurry comprising the cementitious system and water.

The processing profile of a cementitious system is of central importance in the application because it significantly influences the process of processing and the construction progress.

The acceleration of a cementitious system, which may involve the stiffening / hardening and / or hardening of the system, is achieved in the prior art by adding different accelerators as additives. Frequently used accelerators are, for example, calcium chloride, calcium formate or aluminum sulfate ( P. Hewlett, Lea's Chemistry of Cement and Concrete, Chapter 15.6, 4th edition, 1988, Elsevier , or Cheung et al., Cement and Concrete Research 41, 2011, 1289-1309 ). However, the addition of accelerators may, depending on the effectiveness and dosage, reduce the processing time of a cementitious system to the point that it can no longer be processed because the accelerator becomes active immediately after addition of the mixing water. For this reason, some accelerators, such as sodium metaaluminate (NaAlO ₂ ), are virtually unavailable in cementitious systems because they cause too much stiffening.

If no accelerator is used, although the processing time is sufficiently long in cementitious systems, the slow stiffening / solidification delays the construction progress. Both effects together, ie long processing and fast stiffening / hardening, are difficult to achieve with conventional accelerators in cementitious systems, especially when effective accelerators are to be used.

In order to ensure sufficient processing time in cementitious systems despite the use of an accelerator, accelerators have been encapsulated for various applications. Common to the state of the art in encapsulated accelerators is that a separate, external triggering event is necessary for the release of the accelerator, for example a temperature change ( JP2002284555A1 . US6840318B2 . GB1579356 . US7896068B2 ), Ultrasound ( US8047282B2 ) or a pH change ( RU2307145C ). However, there are a number of cementitious systems that can not and should not be influenced externally after application, such as various dry mortars.

For such cementitious systems then an internal trigger is needed, which is indeed activated by mixing with water, but only after a certain time releases the accelerator. In addition, the release time should be able to be controllably changed within certain limits in order to adapt them for different applications.

In the prior art, a suitable internal triggering mechanism is the build-up of osmotic pressure within a coated particle which, after some time, causes the coating to rupture due to swelling in the core, thereby providing rapid drug release. In the pharmaceutical field, some such systems are known, such as from Ghosh, T., et al., Journal of Applied Pharmaceutical Science, 1, 2011, p. 38-49 or B. Amsden, J. Pharm. Pharmaceut. Sci., 10, 2007, pp. 129-143 However, this concept can not be transferred to a cementitious system with pH values of 12 to 13, because the functionality of such coatings no longer exists under these conditions.

In our still unpublished international patent application PCT / EP2012 / 073339 describes coated particles of a controlled release active ingredient at pH values of 10-14 in which the active ingredient is selected from one or more building chemical additives for influencing an inorganic binder, characterized in that the coating of the particles includes shellac. However, in ours PCT / EP2012 / 073339 describe no cementitious systems comprising such cross-linked shellac-coated accelerator particles.

The object underlying the present invention was to substantially avoid the disadvantages of the described prior art. An accelerator should be modified so that, when present in a cementitious system, a long processing time in combination with accelerated stiffening / hardening is achieved. In particular, suitable cementitious systems should be provided to solve this problem.

The above object has been achieved with the features of the independent claims. The dependent claims relate to preferred embodiments. In particular, the above-mentioned object was achieved according to the invention by first converting an accelerator into particles and then applying a coating of shellac, which was subsequently cross-linked. These cross-linked shellac coated accelerator particles are then used as part of a cementitious system.

A first aspect of the present invention accordingly relates to a cementitious system comprising cross-linked shellac coated accelerator particles.

Shellac is a natural substance that is extracted from the excrement of the lacustrine louse ("kerria lacca") by various cleaning processes. From a chemical point of view, shellac is an oligomeric ester composed of about 8 monomeric units and one end of the oligomer carries a free carboxylic acid group. One half of the monomers consists of 9, 10, 16-trihydroxypalmitic acid, which is also referred to as "aleuritic acid". The other half is composed of different terpene acids, which can carry more different chemical groups. The content of free carboxyl groups in shellac is defined by the so-called "acid number", which corresponds to that amount of potassium hydroxide necessary to neutralize one gram of shellac. It is given in mg potassium hydroxide / g shellac and is at many shellacs at about 70 mg / g. Shellac is rendered water-soluble by deprotonation of the carboxylic acid, so that it can be obtained as an ammoniacal aqueous solution with a solids content of about 25%, for example from Harke Group, Mühlheim an der Ruhr, under the name "Aquagold®". Alternatively, the same type shellac in powder form, for example, at the company. Stroever, Bremen, with the type designation "SSB 57" and dissolved with stirring and gentle heating in ammoniacal solution.

The physical transformation of the accelerator into round and smooth particles is the basis for a high-quality coating with a uniform layer thickness and a homogeneous reaction behavior. If the accelerator particles have corners, edges or holes after forming, no uniform coating thickness can be achieved in the subsequent coating process, which in consequence can lead to an inhomogeneous release of the accelerator.

Coating the accelerator particles with cross-linked shellac causes them to rupture under the alkaline conditions of the cementitious system by building up osmotic pressure within the particles after a certain time and releasing the accelerator. Due to the coating, no accelerator is released for a certain time after mixing the cementitious system with water, so that the processing properties are initially unaffected. In addition, partial release of the accelerator during osmotic pressure buildup after release causes rapid reaction with the surrounding cementitious matrix.

The advantages achieved with the present invention thus consist in particular in that the processing properties of a cementitious system are not adversely affected at first by the use of crosslinked shellac-coated accelerator particles, but in the further course achieved by release of the accelerator rapid stiffening / solidification becomes. In addition, by varying the release time of the coated accelerator particles, the stiffening / solidification of a cementitious system can be deliberately changed, resulting in the formulation of cementitious systems further scope. Another advantage is that the release is triggered by an internal mechanism, whereby the cementitious system according to the invention as a conventional cementitious system can be applied without the need for additional external triggers.

The cementitious system according to the invention expediently comprises an inorganic binder selected from Portland cement, high-alumina cement, calcium sulfoaluminate cement, Portland composite cement according to classes CEM II to V, hydraulic binders, latently hydraulic binders, pozzolanic binders, alkalactivatable aluminosilicate binders and gypsum, and mixtures thereof.

Portland cement is probably the best-known hydraulic binder. It was first mentioned in British Patent BP 5022 and has been under constant development ever since. Modern Portland cement contains about 70 wt .-% CaO + MgO, about 20 wt .-% SiO ₂ and about 10 wt .-% Al ₂ O ₃ + Fe ₂ O ₃ .

In addition, there are composite cements based on Portland cement and various accompanying substances, whose composition is regulated in DIN EN 197-1, Table 1 and which are divided into the cement classes CEM II Portland Composite cement, CEM III blastfurnace cement, CEM IV pozzolan cement and CEM V composite cement V. As an accompanying material blast furnace slag, fly ash, pozzolan, trass, silica fume, limestone and others are used. These cements have in common that they have a basic environment by the proportion of Portland cement after mixing with water.

Certain slags from metallurgical processes can be used as admixtures in so-called Portland Kompositzementen, which are also among the hydraulic binders. More generally, hydraulic binders are those inorganic binders that cure even under water.

For example, latent hydraulic binders may be selected from slags, particularly blast furnace slag, blastfurnace slag, granulated blastfurnace, electrothermal phosphor slag, stainless steel slag, and mixtures thereof. These slags can be both industrial slags, ie waste products from industrial processes, as well as synthetically trailing slags. The latter is advantageous because industrial slags are not always available in consistent quantity and quality. For the purposes of the present invention, a latent hydraulic binder is to be understood as meaning preferably an inorganic binder in which the molar ratio of (CaO + MgO): SiO _{2 is} between 0.8 and 2.5, and particularly preferably between 1.0 and 2, 0 is.

Blast furnace slag is a waste product of the blast furnace process. Slag sand is granulated blast furnace slag and blastfurnace slag of finely powdered blastfurnace slag. The blastfurnace flour varies depending on the origin and preparation in its fineness and particle size distribution, the fineness has an influence on the reactivity. As a parameter for the fineness of the so-called Blainewert is used, which is typically in the order of 200 to 1000, preferably between 300 and 500 m ² kg ^-1 . The finer the grinding, the higher the reactivity. The typical composition of the blast furnace slag has already been mentioned at the beginning. Blast furnace slag generally has 30 to 45 wt .-% CaO, about 4 to 17 wt .-% MgO, about 30 to 45 wt .-% SiO ₂ and about 5 to 15 wt .-% Al ₂ O ₃ typically about 40% by weight CaO, about 10% by weight MgO, about 35% by weight SiO ₂ and about 12% by weight Al ₂ O ₃ .

Electro-thermal phosphor slag is a waste product of electrothermal phosphor production. It is less reactive than blast furnace slag and contains about 45 to 50 wt .-% CaO, about 0.5 to 3 wt .-% MgO, about 38 to 43 wt .-% SiO ₂ , about 2 to 5 wt .-% Al ₂ O ₃ and about 0.2 to 3 wt .-% Fe ₂ O ₃ and fluoride and phosphate. Stainless steel slag is a waste product of various steelmaking processes of widely varying composition (see Caijun Shi, Pavel V. Krivenko, Della Roy, Alkali-Activated Cements and Concretes, Taylor & Francis, London & New York, 2006, pp. 42-51 ).

Inorganic binder systems based on reactive water-insoluble compounds based on SiO ₂ in combination with Al ₂ O ₃ , which cure in an aqueous alkaline medium, are also generally known. Such cured binder systems are also referred to as "alkali-activated aluminosilicate binder" or "geopolymers" and are, for example, in US 4,349,386 . WO 85/03699 and US 4,472,199 described. In addition to slags, so-called pozzolanic binders such as, for example, metakaolin, fly ash, activated clay or mixtures thereof can be used as the reactive oxide mixture. The alkaline medium for activation of the binder usually consists of aqueous solutions of alkali metal carbonates, alkali fluorides, alkali metal hydroxides and / or soluble water glass. In EP2504296 A1 describes systems in which the binder cures in the form of a hybrid matrix in which a calcium silicate hydrate matrix and a geopolymer matrix are in appropriate proportion and interpenetrate so that the overall matrix is both acid resistant and alkali resistant.

The pozzolanic binder is selected, for example, from amorphous silica, preferably precipitated silica, fumed silica and microsilica, glass flour, fly ash, preferably lignite fly ash and coal fly ash, metakaolin, natural pozzolans such as tuff, trass and volcanic ash, natural and synthetic zeolites, and mixtures thereof. An overview of the invention suitable pozzolanic binder is found for example Caijun Shi, Pavel V. Krivenko, Della Roy, Alkali-Activated Cements and Concretes, Taylor & Francis, London & New York, 2006, pp. 51-63 , The test for pozzolanic activity can be carried out according to DIN EN 196 part 5.

The amorphous silica is preferably an X-ray amorphous silica, ie a silica which does not show crystallinity in the powder diffraction process. For the purposes of the present invention, glass flour is also to be regarded as amorphous silica. The amorphous silica according to the invention expediently has a content of at least 80% by weight, preferably at least 90% by weight, of SiO ₂ . Precipitated silica is obtained on a large scale via precipitation processes starting from water glass. Precipitated silica is also called silica gel, depending on the manufacturing process. Pyrogenic silica is produced by reaction of chlorosilanes such as silicon tetrachloride in the oxyhydrogen flame. Pyrogenic silica is an amorphous SiO ₂ powder with a particle diameter of 5 to 50 nm and a specific surface area of 50 to 600 m ² g ^-1 .

Microsilica is a by-product of silicon or ferrosilicon production and also consists largely of amorphous SiO ₂ powder. The particles have diameters in the order of 0.1 microns. The specific surface area is on the order of 15 to 30 m ² g ^-1 . In contrast, commercially available quartz sand is crystalline and has comparatively large particles and a comparatively small specific surface area. It serves according to the invention as an inert additive.

Fly ashes are caused, among other things, by the burning of coal in power plants. Fly ash class C contains according to WO 08/012438 about 10% by weight of CaO, whereas flyashes of class F contain less than 8% by weight, preferably less than 4% by weight and typically about 2% by weight of CaO.

Metakaolin is formed during the dehydrogenation of kaolin. While kaolin releases physically bound water at 100 to 200 ° C, dehydroxylation occurs at 500 to 800 ° C with collapse of the lattice structure and formation of metakaolin (Al ₂ Si ₂ O ₇ ). Pure metakaolin accordingly contains about 54% by weight of SiO ₂ and about 46% by weight of Al ₂ O ₃ .

The collective term "gypsum" is understood as meaning the modifications CaSO ₄ (anhydrite), CaSO ₄ .0.5 H ₂ O (hemihydrate) and CaSO ₄ .2 H ₂ O (gypsum). The first two modifications harden when adding water, so they are inorganic binders, while gypsum does not harden. However, it can be used as sulfate source in said inorganic binders.

Unlike our above PCT / EP2012 / 073339 in the "cementitious system" of the invention, the presence of a cementitious component is required. The crosslinked shellac-coated promoter particles may be in the form of a one-part formulation in the cementitious component or from the cementitious component Component be kept separately (so-called "kit of parts"). The Portland cement and / or Portlandkompositzement is present in principle and is useful to more than 3 wt .-%, preferably more than 10 wt .-% and in particular more than 25 wt .-% in the inventive cementitious system.

Furthermore, the shellac coating contains preferably more than 50 wt .-% shellac, more preferably more than 80 wt .-% and in particular more than 95 wt .-%.

The cementitious system according to the invention is further characterized in that the shellac coating contains up to 10% by weight, preferably up to 5% by weight, of urea, based on the shellac portion.

The cementitious system according to the invention is further characterized in that the shellac coating contains suitably 0 to 30 wt .-%, preferably 0 to 15 wt .-% and in particular 0 to 5 wt .-% filler, based on the shellac portion contains ,

The said filler is suitably made of natural or precipitated calcium carbonate, amorphous, crystalline or fumed silica, aluminum silicate, e.g. Kaolin or mica, magnesium silicate hydrate, aluminum hydroxide and magnesium hydroxide, and mixtures thereof.

The release time of the accelerator generally depends on the degree of crosslinking of the shellac, the shellac coating thickness, the accelerator content, the particle design, and the accelerator itself, and can be adapted to the particular application in the cementitious system.

The shellac according to the invention is expediently present in a form crosslinked by thermal treatment, treatment with microwaves, electric plasma, high-energy particles and / or ionizing radiation. The shellac is preferably present in a form crosslinked by thermal treatment of from 1 hour to 7 days, preferably from 1 hour to 2 days, at temperatures of from 80.degree. C. to 140.degree. C., preferably from 100.degree. C. to 120.degree.

Furthermore, the inventive cementitious system is characterized in that the accelerator is expediently selected from salts of elements of the main groups 1 to III and mixtures thereof, preferably lithium salts, in particular lithium sulfate, sodium salts and potassium salts, in particular sodium and potassium silicates and water glasses, magnesium salts, Calcium salts, in particular calcium chloride, calcium nitrate, calcium formate, calcium silicate, calcium silicate hydrate and ettringite, and aluminum salts, in particular sodium metaaluminate (NaAlO ₂ ) and aluminum sulfate.

The accelerator particles should have an average particle diameter of 50 to 1000 μm, preferably 100 to 300 μm, while the shellac coating of the accelerator particles should have an average thickness of 1 to 80 μm, preferably 1 to 30 μm.

The cross-linked shellac coated accelerator particles suitably comprise at least two layers in a core / shell structure, the core containing the accelerator and the coating containing the crosslinked shellac.

The cementitious system according to the invention is preferably characterized in that the accelerator is applied to a carrier, adsorbed to a carrier, absorbed in a carrier or mixed with a carrier. The carrier in this definition is synonymous with the excipient used to construct the particle nucleus. In the case of application, e.g. Quartz sand, glass beads or other unreactive, particulate material with suitable grain size. For example, in the case of adsorption, the carrier may be a particulate porous material, e.g. Diatomaceous earth, porous silica, Circosil, a synthetic product of calcium silicate hydrate, cellulose particles or a zeolitic material. In the case where the carrier is mixed with the accelerator, the carrier is, for example, calcium carbonate, talc, or another excipient capable of being formed into a suitable substrate with the accelerator.

The cementitious system according to the invention is further characterized in that the accelerator particles additionally preferably contain a diffusion control layer and / or a barrier layer within the shellac coating. The diffusion control layer is preferably methyl cellulose, while the barrier layer is preferably sodium sulfate. The advantage of a diffusion control layer is that it retards the water uptake and thus the time of bursting of the coated accelerator particles due to osmotic pressure. The advantage of a barrier layer such as sodium sulfate is that the possibly aggressive accelerator (such as NaAlO ₂ ) is not in direct contact with the chemically sensitive shellac.

The proportion of active ingredient can be varied by targeted selection of the structure of the substrate for the accelerator, so that a local overdose of the cementitious system with accelerator can be avoided. Local overdosage should be avoided to avoid secondary adverse reactions through subsequent activation by excess accelerators.

The cementitious system according to the invention is further characterized in that the crosslinked shellac-coated accelerator particles, based on the inorganic binder, expedient to 0.1 to 5.0 wt .-%, preferably 0.3 to 3.0 parts by weight. % and in particular 0.5 to 2.0 wt .-% are present.

In the cementitious system of the present invention, the accelerator particles coated with crosslinked shellac are preferably contained in the form of a one-component formulation in the cementitious component containing the inorganic binder. In particular, this is a dry mortar. In such dry mortars Portland cement is preferably used as the inorganic binder.

Alternatively, in the cementitious system of the present invention, the accelerator particles coated with crosslinked shellac may be present in an additive component separately held by the cementitious component containing the inorganic binder.

Accordingly, another object of the present invention is directed to the use of the additive component of the invention for curing the cementitious component containing the inorganic binder.

Another object of the present invention is the use of the additive component of the invention as an accelerator for the inventive cementitious system.

Finally, another object of the present invention is a cement slurry comprising the cementitious system of the invention and water. This cement slurry expediently has a water / cement value (w / c) of from 0.1 to 1.0, preferably from 0.2 to 0.7 and in particular from 0.3 to 0.6.

Fig. 1

die jeweiligen Freisetzungscharakteristiken von unterschiedlich beschichteten Lithiumsulfat-Teilchen in synthetischer Porenlösung,

Fig. 2

die Freisetzungscharakteristik von mit Schellack beschichteten Lithiumsulfat-Teilchen nach Lagerung bei Raumtemperatur,

Fig. 3

die Freisetzung von mit Schellack beschichtetem Lithiumsulfat, geträgert auf Glasperlen, nach unterschiedlich langer thermischer Behandlung bei 100 °C,

Fig. 4

die Freisetzung von thermisch nachbehandelten Lithiumsulfat-Teilchen mit Schellack-Beschichtung nach längerer Lagerung bei Raumtemperatur

Fig. 5

die Veränderung der Freisetzungscharakteristik von mit Schellack beschichteten Teilchen in Abhängigkeit von den Quervernetzungsbedingungen, und

Fig. 6

den Aufbau eines mit Schellack beschichteten Beschleunigerteilchens aus Beispiel 3.

The present invention will now be further elucidated with reference to the following examples and with reference to the accompanying drawings. In the drawings shows:

Fig. 1

the respective release characteristics of differently coated lithium sulfate particles in synthetic pore solution,

Fig. 2

the release characteristics of shellac-coated lithium sulfate particles after storage at room temperature,

Fig. 3

the release of shellac-coated lithium sulphate, supported on glass beads, after thermal treatment at 100 ° C. for different lengths of time,

Fig. 4

the release of thermally post-treated lithium sulfate particles with shellac coating after prolonged storage at room temperature

Fig. 5

the change in the release characteristics of shellac-coated particles depending on the crosslinking conditions, and

Fig. 6

the structure of a shellac-coated accelerator particle from Example 3.

Examples Example 1 (reference)

In Fig. 1 It can be seen that lithium sulfate particles coated with uncrosslinked shellac, in contrast to lithium sulfate particles coated with wax, polyvinyl acetate or water glass, exhibit a step-shaped release characteristic in the alkaline medium. The lithium sulfate release was measured with a conductivity electrode in synthetic pore solution. This was a synthetically prepared alkaline solution with a pH of about 12.5, which was saturated with Ca ²⁺ and also contained Na ⁺ , K ⁺ and SO ₄ ^2- and a squeezed pore solution of a Portland cement Water mixture resembled. As the substrate, lithium sulfate particles having a particle size of 750 μm in diameter were used, which had been produced by extrusion and rounding on a turntable.

Example 2

After prolonged storage at room temperature of the shell-lacquered lithium sulfate particles, a step-like release characteristic was as before, but the release time was significantly prolonged ( Fig. 2 ), indicating aging of the coating. As was later shown, the aging was a subsequent esterification of the -OH and carboxyl groups in the shellac, ie crosslinking. It was also shown that the crosslinking could be promoted by storage at elevated temperature (100 ° C.) for one or more days, see Fig. 3 , In addition, no appreciable aging occurred after the thermal treatment, such as Fig. 4 shows. However, when the shellac coating was carried out too long or at too high a temperature, the coating lost the step-like release characteristics and approached a diffusion-controlled release (FIG. Fig. 5 ).

Example 3

The stiffening was based on DIN EN 1015-9 on the temporal force increase when pressing a circular brass rod with a diameter of 6.175 mm and a penetration depth of 25 mm measured in a cementitious system. The measured weight values were converted into N / mm ² , the gravitational acceleration being assumed to be 10 m / s ² . The times when penetrating resistances of 0.5 or 3.5 N / mm ² were exceeded were extrapolated from the respectively adjacent values and, contrary to DIN EN 1015-9, rounded to 5 min.

• 360 g Wasser
• 800 g Quarzsand (Typ BCS 412 von der Fa. Strobel Quarzsande, mittlere Korngröße 120 µm)
• 800 g Zement (Milke CEM I 52,5R)

As a cementitious reference system was used:

• 360 g of water
• 800 g of quartz sand (type BCS 412 from the company Strobel Quarzsande, mean particle size 120 μm)
• 800 g of cement (Milke CEM I 52.5R)

• Natriummetaaluminat (NaAlO₂), 53-55 % Al₂O₃-Gehalt, fein gemahlen, unstabilisiert, von der Fa. BK Giulini, Ludwigshafen,
• Mit quervernetztem Schellack beschichtete Natriummetaaluminat-Teilchen gemäß nachstehender Herstellung mit unterschiedlichen Freisetzungszeiten von ca. 15 min, im Weiteren "Beschleuniger Teilchen I" genannt, bzw. 45 min, im Weiteren "Beschleuniger Teilchen II" genannt. Die Freisetzungszeiten der Beschleuniger-Teilchen I und II wurden über die Veränderung der Leitfähigkeit in synthetischer Porenlösung bei Raumtemperatur gemessen.

The accelerator used was:

• Sodium metaaluminate (NaAlO ₂ ), 53-55% Al ₂ O ₃ content, finely ground, unstabilized, from BK Giulini, Ludwigshafen,
• Cross-linked shellac coated sodium metaaluminate particles according to the following production with different release times of about 15 min, hereinafter referred to as "accelerator particle I", or 45 min, hereinafter referred to as "accelerator particle II". The release times of the accelerator particles I and II were measured by changing the conductivity in synthetic pore solution at room temperature.

The preparation of the accelerator particles took place in three process steps:

granulation

In a first step, sodium metaaluminate (53-55% Al ₂ O ₃ content, finely ground, unstabilized from BK Giulini, Ludwigshafen) with quartz sand (type BCS 412 from Strobel Quarzsande, mean particle size 120 μm) and Water in an intensive mixer from Eirich converted into a granulate. In this process step, the sodium metaaluminate attracted to the grains of sand and formed largely rounded particles. After drying the granules at 100 ° C was separated by screening oversize and undersize outside the range of 200-300 microns.

coating

The prepared granules were then transferred to a fluidized bed coater (type "Unilab" Fa. Bosch / Hüttlin) and there first with sodium sulfate and then with shellac (type SSB 57, Fa. Ströver Bremen) at a product temperature of about 30-35 ° C. coated. The sodium sulfate solution used had a solids content of 15% by weight. The shellac was dissolved in ammoniacal solution before coating and adjusted to a solids content of 10% by weight.

Thermal crosslinking

In this example, crosslinking of the shellac was accomplished by storage of the accelerator particles at 100 ° C for 24 and 75 hours, respectively. In structure, the accelerator particles I and II do not differ. For storage, the accelerator particles were mixed with a fine particulate inorganic powder (calcium carbonate) having an average particle size of about 5 microns in equal parts by weight in order to prevent sticking of the particles during storage. After storage, the excipient was separated again on a tumbler with a mesh size of <150 microns. The structure of the accelerator particles I and II is in Fig. 6 played.

The mean grain size of the accelerator particles I and II was about 240 microns. The contents of the coated accelerator particles were about 33 wt .-% quartz sand, 33 wt .-% sodium metaaluminate, 12 wt .-% sodium sulfate (anhydrous), 22 wt .-% shellac (data rounded).

The reference system was mixed according to EN 196-1. The experiments and measurements were carried out at 23 ° C and 50% rel. Humidity was carried out and the materials used and the test device was equilibrated for 24 h in this climate. The zero point of the subsequent measurement was the time of mixing the cement with the mixing water. The results are shown in Table 1. The dosage of the accelerator is given in weight percent, based on the weight of the cement. The respective penetration resistance is given in [N / mm ² ], times are given in minutes. Table 1: Test results of the cementitious system based on DIN EN 1015-9 Dosing of the accelerator Penetration resistance after mixing Time up to a penetration resistance of 0.5 Time up to a penetration resistance of 3.5 Δ t between penetration resistance 0.5 and 3.5 0.0% 0.01 140 215 75 0.5% NaAlO ₂ 0.22 15 85 70 0.5% particles I 0.01 100 180 80 0.5% particles II 0.01 120 190 70 1.0% NaAlO ₂ not processable not processable not processable - 1.0% particles I 0.01 55 110 55 1.0% Particles II 0.01 110 165 55

The example shows that the accelerator particles I and II compared to the non-coated accelerator according to the invention show a prolonged processing time and an accelerated stiffening / solidification compared to the reference system without accelerator. At a higher dosage of the accelerator of 1 wt .-%, moreover, a faster stiffening / solidification can be observed.

Claims (23)

A cementitious system comprising cross-linked shellac-coated accelerator particles. A cementitious system according to claim 1 comprising an inorganic binder selected from Portland cement, alumina cement, calcium sulfoaluminate cement, Portland composite cement according to classes CEM II to V, hydraulic binders, latent hydraulic binders, pozzolanic binders, alkalactivatable aluminosilicate binders and gypsum, and mixtures thereof. Cementitious system according to claim 1 or 2, characterized in that the Portland cement and / or Portlandkompositzement to more than 3 wt .-%, preferably more than 10 wt .-% and in particular more than 25 wt .-% is included. Cementitious system according to one of claims 1 to 3, characterized in that the shellac coating contains more than 50 wt .-% shellac, preferably more than 80 wt .-% and in particular more than 95 wt .-%. Cementary system according to one of claims 1 to 4, characterized in that the shellac coating contains up to 10 wt .-%, preferably up to 5 wt .-% urea, based on the shellac content. Cementitious system according to one of claims 1 to 5, characterized in that the shellac coating 0 to 30 wt .-%, preferably 0 to 15 wt .-% and in particular 0 to 5 wt .-% filler, based on the shellac Share, contains. A cementitious system according to claim 6, characterized in that the filler is selected from natural or precipitated calcium carbonate, amorphous, crystalline or fumed silica, aluminum silicate such as kaolin or mica, magnesium silicate hydrate, aluminum hydroxide and magnesium hydroxide, and mixtures thereof. Cementitious system according to one of claims 1 to 7, characterized in that the shellac is present in a form crosslinked by thermal treatment, treatment with microwaves, electric plasma, high-energy particles and / or ionizing radiation. A cementitious system according to claim 8, characterized in that the shellac is in a thermal treatment of 1 h to 7 days, preferably 1 h to 2 days, at temperatures from 80 ° C to 140 ° C, preferably from 100 ° C to 120 ° C, cross-linked form. Cementitious system according to one of claims 1 to 9, characterized in that the accelerator is selected from salts of elements of the main groups I - III and mixtures thereof, preferably from lithium salts, in particular lithium sulfate, sodium salts and potassium salts, in particular sodium and potassium silicates and water glasses, Magnesium salts, calcium salts, especially calcium chloride, calcium nitrate, calcium formate, calcium silicate, calcium silicate hydrate and ettringite, and aluminum salts, especially sodium metaaluminate (NaAlO ₂ ) and aluminum sulfate. Cementitious system according to one of claims 1 to 10, characterized in that the accelerator particles have an average particle diameter of 50 to 1000 microns, preferably from 100 to 300 microns. Cementitious system according to one of claims 1 to 11, characterized in that the shellac coating of the accelerator particles has an average thickness of 1 to 80 microns, preferably from 1 to 30 microns. A cementitious system according to any one of claims 1 to 12, characterized in that the crosslinked shellac-coated accelerator particles include at least two layers in a core / shell structure, the core containing the accelerator and the coating containing the crosslinked shellac. Cementitious system according to claim 13, characterized in that the accelerator is applied to a carrier, adsorbed to a carrier, absorbed in a carrier or mixed with a carrier. Cementitious system according to one of claims 13 or 14, characterized in that the accelerator particles additionally contain a diffusion control layer, preferably of methylcellulose, and / or a barrier layer, preferably of sodium sulphate, within the shellac coating. A cementitious system according to any one of claims 1 to 15, characterized in that the cross-linked shellac-coated accelerator particles, based on the inorganic binder, to 0.1 to 5.0 wt .-%, preferably 0.3 to 3.0 Wt .-% and in particular 0.5 to 2.0 wt .-% present. A cementitious system according to any one of claims 1 to 16, characterized in that the cross-linked shellac-coated accelerator particles are contained in the form of a one-component formulation in the inorganic binder-containing cementitious component. Cementitious system according to claim 17, characterized in that it is a dry mortar. A cementitious system according to any one of claims 1 to 16, characterized in that the accelerator particles coated with crosslinked shellac are present in an additive component separately held by the cementitious component containing the inorganic binder. Use of the additive component according to claim 19 for curing the cementitious component containing the inorganic binder. Use of the additive component according to claim 19 as accelerator for the cementitious system according to the definition of one of the preceding claims 1 to 19. A cement slurry comprising the cementitious system as defined in any one of claims 1 to 19 and water. Cement slurry according to claim 22 having a water / cement value (w / c) of from 0.1 to 1.0, preferably from 0.2 to 0.7 and in particular from 0.3 to 0.6.

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